Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to, in the presence of ammonia (NH3), convert NOx (NO and NO2 in some fraction) into harmless nitrogen gas (N2) and water vapor (H2O).
In order to meet increasingly strict NOx emission requirements and regulations, the concentration of the NOx gas in the exhaust gas emerging from the engine is estimated to control the operation of the aftertreatment system, for example the SCR system included in the aftertreatment system. For example, based on the estimated engine NOx amount, an amount of reductant to be inserted into the SCR system can be controlled and/or a temperature of the SCR system can be controlled. The estimated engine NOx amount can be estimated based on one or more engine operational parameters, for example engine speed, load, lean or rich operating conditions, fueling conditions, etc.
The estimated NOx concentration in the exhaust gas produced by the engine is adjusted for the amount of oxygen in the exhaust gas. In a number of conventional aftertreatment systems, the estimated engine NOx amount is adjusted using an oxygen concentration measured from a physical oxygen sensor. However, the inclusion of a physical oxygen sensor increases the cost of the system, and the reliability of the system is subject to the oxygen sensor functioning properly.